Projectors of structured light

ABSTRACT

An optoelectronic device includes a semiconductor substrate and a monolithic array of light-emitting elements, including first and second sets of the light-emitting elements arranged on the substrate in respective first and second two-dimensional patterns, which are interleaved on the substrate. First and second conductors are respectively connected to separately drive the first and second sets of the light-emitting elements so that the device selectably emits light in either or both of the first and second patterns.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.15/265,877, filed Sep. 15, 2016, which is a continuation of U.S. patentapplication Ser. No. 14/242,895, filed Apr. 2, 2014, which is acontinuation of U.S. patent application Ser. No. 13/567,095, filed Aug.6, 2012, which claims the benefit of U.S. Provisional Patent Application61/521,406, filed Aug. 9, 2011, and U.S. Provisional Patent Application61/611,075, filed Mar. 15, 2012. Both of these related applications areincorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates generally to optical and optoelectronicdevices, and specifically to devices for projection of patterns.

BACKGROUND OF THE INVENTION

Compact optical projectors are used in a variety of applications. Forexample, such projectors may be used to cast a pattern of coded orstructured light onto an object for purposes of three-dimensional (3D)mapping (also known as depth mapping). In this regard, U.S. PatentApplication Publication 2008/0240502, whose disclosure is incorporatedherein by reference, describes an illumination assembly in which a lightsource, such as a laser diode or LED, transilluminates a transparencywith optical radiation so as to project a pattern onto the object. (Theterms “optical” and “light” as used in the present description and inthe claims refer generally to any and all of visible, infrared, andultraviolet radiation.) An image capture assembly captures an image ofthe pattern that is projected onto the object, and a processor processesthe image so as to reconstruct a 3D map of the object.

PCT International Publication WO 2008/120217, whose disclosure isincorporated herein by reference, describes further aspects of the sortsof illumination assemblies that are shown in the above-mentioned US2008/0240502. In one embodiment, the transparency comprises an array ofmicro-lenses arranged in a non-uniform pattern. The micro-lensesgenerate a corresponding pattern of focal spots, which is projected ontothe object.

Optical projectors may, in some applications, project light through oneor more diffractive optical elements (DOEs). For example, U.S. PatentApplication Publication 2009/0185274, whose disclosure is incorporatedherein by reference, describes apparatus for projecting a pattern thatincludes two DOEs that are together configured to diffract an input beamso as to at least partially cover a surface. The combination of DOEsreduces the energy in the zero-order (undiffracted) beam. In oneembodiment, the first DOE generates a pattern of multiple beams, and thesecond DOE serves as a pattern generator to form a diffraction patternon each of the beams. A similar sort of arrangement is described in U.S.Patent Application Publication 2010/0284082, whose disclosure is alsoincorporated herein by reference.

As another example, U.S. Patent Application Publication 2011/0188054,whose disclosure is incorporated herein by reference, describesphotonics modules that include optoelectronic components and opticalelements in a single integrated package. In one embodiment, anintegrated photonics module (IPM) comprises radiation sources in theform of a two-dimensional matrix of optoelectronic elements, which arearranged on a substrate and emit radiation in a direction perpendicularto the substrate. Such an IPM typically comprises multiple, parallelrows of emitters, such as light-emitting diodes (LEDs) orvertical-cavity surface-emitting laser (VCSEL) diodes, forming a grid inthe X-Y plane. The radiation from the emitters is directed into anoptical module, comprising a suitable patterned element and a projectionlens, which projects the resulting pattern onto a scene.

SUMMARY OF THE INVENTION

Embodiments of the present invention that are described hereinbelowprovide improved devices and methods for projection of patterned light.

There is therefore provided, in accordance with an embodiment of thepresent invention, optical apparatus, including a beam source, which isconfigured to generate an optical beam having a pattern imposed thereon.A projection lens is configured to receive and project the optical beamso as to cast the pattern onto a first area in space having a firstangular extent. A field multiplier is interposed between the projectionlens and the first area and is configured to expand the projectedoptical beam so as to cast the pattern onto a second area in spacehaving a second angular extent that is at least 50% greater than thefirst angular extent.

Typically, the second angular extent is at least twice the first angularextent.

The apparatus may include a reflective surface interposed so as to foldthe projected optical beam between the projection lens and the fieldmultiplier.

In some embodiments, the field multiplier includes a diffractive opticalelement (DOE). The DOE is typically configured to expand the projectedoptical beam by producing multiple, mutually-adjacent tiles on thesecond area, each tile containing a respective replica of the pattern.In disclosed embodiments, the DOE is configured to generate atwo-dimensional array of the tiles. The tiles have a pitch, and in oneembodiment, at least some of the tiles are offset transversely relativeto neighboring tiles by an offset that is a fraction of the pitch.

In other embodiments, the field multiplier includes a prism. Typically,the prism has an edge and is positioned so that the optical beamprojected by the projection lens is incident on the edge. In oneembodiment, the prism has a triangular profile with a vertex angle thatis greater than 90° at the edge upon which the projected optical beam isincident. Alternatively or additionally, the field multiplier mayinclude first and second prisms, having respective first and secondedges and having respective first and second bases opposite the firstand second edges, wherein the first and second bases are joined togetherwhile the first and prisms are rotated so that the first and secondedges opposite the bases are mutually perpendicular. Furtheralternatively or additionally, the prism may have a pyramidal shape withan apex and is positioned so that the optical beam projected by theprojection lens is incident on the apex. The prism may include aninternal reflective surface configured to fold the projected opticalbeam.

In some embodiments, the beam source includes a light source, whichemits the optical beam, and a patterning element, which is interposed inthe optical beam emitted by the light source. In other embodiments, thebeam source includes a monolithic array of light-emitting elements,arranged on a semiconductor substrate in a two-dimensional patterncorresponding to the pattern imposed on the optical beam.

There is also provided, in accordance with an embodiment of the presentinvention, an optoelectronic device, including a semiconductor substrateand a monolithic array of light-emitting elements, arranged on thesubstrate in a two-dimensional pattern that is not a regular lattice.

In a disclosed embodiment, the light-emitting elements includevertical-cavity surface-emitting laser (VCSEL) diodes.

In some embodiments, the two-dimensional pattern of the light-emittingelements is an uncorrelated pattern.

In one embodiment, the light-emitting elements include first and secondsets of the light-emitting elements, wherein the first and second setsare interleaved on the substrate in respective first and secondpatterns, and wherein the device includes first and second conductors,which are respectively connected to separately drive the first andsecond sets of the light-emitting elements so that the device selectablyemits light in either or both of the first and second patterns. Thedevice may further include projection optics, which are configured toproject the light emitted by the light emitting elements onto an object,and an imaging device, which is configured to capture images of theobject in a low-resolution mode while only the first set of thelight-emitting elements is driven to emit the light, thereby projectinga low-resolution pattern onto the object, and in a high-resolution modewhile both of the first and second sets of the light-emitting elementsare driven to emit the light, thereby projecting a high-resolutionpattern onto the object.

In some embodiments, the device includes a projection lens, which ismounted on the semiconductor substrate and is configured to collect andfocus light emitted by the light-emitting elements so as to project anoptical beam containing a light pattern corresponding to thetwo-dimensional pattern of the light-emitting elements on the substrate.The device may also include a diffractive optical element (DOE), whichis mounted on the substrate and is configured to expand the projectedoptical beam by producing multiple, mutually-adjacent replicas of thepattern. The projection lens and the DOE may be formed on opposing sidesof a single optical substrate.

Alternatively, the device includes a single diffractive optical element(DOE), which is mounted on the semiconductor substrate and is configuredto collect and focus light emitted by the light-emitting elements so asto project an optical beam containing a light pattern corresponding tothe two-dimensional pattern of the light-emitting elements on thesubstrate while expanding the projected optical beam by producingmultiple, mutually-adjacent replicas of the pattern.

There is additionally provided, in accordance with an embodiment of thepresent invention, a method for pattern projection, which includesgenerating an optical beam having a pattern imposed thereon. The opticalbeam is projected using a projection lens so as to cast the pattern ontoa first area in space having a first angular extent. A field multiplieris applied to expand the optical beam projected by the projection lensso as to cast the pattern onto a second area in space having a secondangular extent that is at least 50% greater than the first angularextent.

There is further provided, in accordance with an embodiment of thepresent invention, a method for producing an optoelectronic device. Themethod includes providing a semiconductor substrate and forming amonolithic array of light-emitting elements on the substrate in atwo-dimensional pattern that is not a regular lattice.

The present invention will be more fully understood from the followingdetailed description of the embodiments thereof, taken together with thedrawings in which:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic side view of a 3D mapping system, in accordancewith an embodiment of the present invention;

FIG. 2 is a block diagram that schematically illustrates a projectionassembly, in accordance with an embodiment of the present invention;

FIGS. 3A and 3B are schematic side views of projection assemblies, inaccordance with embodiments of the present invention;

FIG. 4A is a schematic, pictorial illustration of a field multiplierprism, in accordance with an embodiment of the present invention;

FIG. 4B is a schematic, geometrical representation of the prism of FIG.4A;

FIG. 4C is a schematic plot showing angular characteristics of a fieldmultiplier prism, in accordance with an embodiment of the presentinvention;

FIG. 5 is a schematic side view of a projection assembly, in accordancewith an embodiment of the present invention;

FIGS. 6 and 7 are schematic, pictorial illustrations of field multiplierprisms, in accordance with embodiments of the present invention;

FIG. 8 is a schematic top view of a semiconductor die on which apatterned emitter array has been formed, in accordance with anembodiment of the present invention;

FIGS. 9A-9C are schematic side views of integrated optical projectionmodules, in accordance with embodiments of the present invention;

FIGS. 10A and 10B are schematic frontal views of patterns projected byoptical projection modules in accordance with embodiments of the presentinvention; and

FIG. 11 is a schematic top view of a semiconductor die on which apatterned emitter array has been formed, in accordance with analternative embodiment of the present invention.

DETAILED DESCRIPTION OF EMBODIMENTS Overview

In many optical projection applications, a pattern must be projectedover a wide angular range. For example, in the sort of 3D mappingapplications that are described above in the Background section, it isoften desirable that the pattern of light that is used to create the mapbe projected over a field of 90° or more. In conventional opticaldesigns, achieving reasonable optical quality over such a wide field ofview (FOV) requires the use of costly, multi-element projection optics.Both the cost and the size of such optics can be prohibitive forconsumer applications, which generally require compact, inexpensivesolutions.

Some embodiments of the present invention that are described hereinbelowaddress these demands by means of a field multiplier, which follows theprojection optics in the optical train and expands the field over whicha desired pattern is projected, while maintaining the optical quality ofthe projected pattern. The addition of the field multiplier makes itpossible to project a pattern over a wide area using compact,inexpensive projection optics, which themselves have a relatively narrowFOV.

In the disclosed embodiments, optical apparatus comprises a beam source,which generates a patterned optical beam. A projection lens projects thepatterned optical beam and would, in the absence of the fieldmultiplier, cast the pattern onto a given area in space having a certainangular extent, corresponding to the field of view (FOV) of theprojection lens. (The term “lens,” as used in the context of the presentdescription and in the claims, refers to both simple and compound,multi-element lenses unless explicitly stated otherwise.) The fieldmultiplier is interposed in the FOV of the projection lens—between thelens and the given area in space—and expands the projected beam so thatthe pattern is cast onto an area in space having an angular extent thatis at least 50% greater than the FOV of the projection lens. Dependingon design, the expanded beam following the field multiplier can havetwice the FOV of the projection lens, or even more.

The use of a field multiplier in the manner described above also makesit possible to interpose a reflective surface between the projectionlens and the field multiplier, thus folding the projected optical beam.In this configuration, the axis of the beam source and projection opticsmay be oriented perpendicular to the axis of the expanded, projectedbeam. The option of folding the beam in this manner can be useful inapplications in which space is at a premium.

The field multiplier may be implemented in various different ways, whichare described in detail hereinbelow. For example, the field multipliermay comprise a diffractive optical element (DOE) or a prism.

In some embodiments, the beam source comprises a light source, whichemits the optical beam, and a patterning element, such as a microlensarray, which is interposed in the optical beam emitted by the lightsource. In other embodiments, the beam source comprises a monolithicarray of light-emitting elements, which are arranged on a semiconductorsubstrate in a two-dimensional pattern corresponding to the pattern tobe imposed on the optical beam.

System Description

FIG. 1 is a schematic side view of a 3D mapping system 20, in accordancewith an embodiment of the present invention. System 20 is described hereas an example of the use of the sorts of field multipliers that aredescribed below, and not by way of limitation. The principles of thepresent invention may similarly be applied in other sorts of opticalprojection systems that require a wide FOV and can benefit from theadvantages of compactness and low cost that are offered by the disclosedembodiments.

System 20 comprises a projection assembly 30, which projects a patternedbeam 38 onto the surface of an object 28—in this example the hand of auser of the system. An imaging assembly 32 captures an image of theprojected pattern on the surface and processes the image so as to derivea 3D map of the surface. For this purpose, assembly 32 typicallycomprises objective optics 40 and an image sensor 42, which captures theimage, as well as a digital processor (not shown), which processes theimage to generate the 3D map. Details of the image capture andprocessing aspects of system 20 are described, for example, in theabove-mentioned U.S. Patent Application Publication 2010/0118123, aswell as in U.S. Patent Application Publication 2010/0007717, whosedisclosure is incorporated herein by reference.

Projection assembly 30 comprises a patterned beam generator 34, whichprojects a patterned illumination beam with a certain FOV, and a fieldmultiplier 36, which expands the projected beam to created patternedbeam 38 with a wider FOV. In this example, the pattern compriseshigh-contrast light spots on a dark background, in a random orquasi-random arrangement, as explained in the above-mentioned patentapplication publications. Alternatively, any other suitable type ofpattern (including images) may be projected in this fashion.

FIG. 2 is a block diagram that schematically illustrates functionalcomponents of projection assembly 30, in accordance with an embodimentof the present invention. Assembly 30 comprises a beam source, whichgenerates an optical beam having a pattern imposed on it.

In this embodiment, the beam source comprises a number of separateelements, including a light source 50, which produces an unpatternedbeam, and a patterning element 52, which imposes the desired pattern onthe beam. Patterning element 52 may comprise, for example, atransparency containing the desired pattern; or a microlens array, inwhich the microlenses are disposed on a transparent substrate in anon-uniform arrangement corresponding to the desired pattern; or asuitable diffractive optical element (DOE); or any other suitablepatterning element that is known in the art. In alternative embodiments,as shown below in FIG. 8, for example, the beam source may comprise anon-uniform array of light sources, which are disposed on a substrate inan arrangement corresponding to the desired pattern (in which case thefunctions of light source 50 and patterning element 52 are embodiedtogether in a single, integrated device).

A projection lens 54 receives and projects the patterned beam from thebeam source, thus generating a projected beam with a narrow FOV, ofangular extent 2w (wherein w is the half field angle and “narrow” isrelative to the greater FOV of patterned beam 38). Optionally, a beamfolder 56, typically comprising a reflective surface, is interposed soas to fold the projected optical beam that is output by lens 54. Folder56 typically turns the beam axis by 90°, but may alternatively beconfigured for larger or smaller folding angles. A field multiplier 36expands the projected beam to give the greater FOV, of angular extent2ω′, of patterned output beam 38.

Diffractive Field Multipliers

Reference is now made to FIGS. 3A and 3B, which are schematic side viewsof projection assembly 30, in accordance with two embodiments of thepresent invention. The embodiments are largely similar to one another,except that the embodiment of FIG. 3B includes a mirror serving as beamfolder 56 interposed between projection lens 54 and field multiplier 36.The field multiplier in both embodiments comprises a diffractive opticalelement (DOE), which is positioned in the exit pupil of lens 54. Thislocation of field multiplier 36 is useful in reducing the required sizeof the DOE.

Light source 50 in these embodiments comprises, by way of example, alaser diode or light-emitting diode (LED), or an array of such diodes,in an integrated package. A collection lens 58 collimates the lightemitted by the light source, and this collimated light transilluminatespatterning element 52, which in this embodiment comprises a microlensarray. The microlens array creates a non-uniform pattern of focal spotsin its rear focal plane, and this pattern is projected by projectionlens 54.

The pattern projected by projection lens 54 is multiplied by the DOE,which creates multiple, mutually-adjacent tiles, each containing arespective replica of the original pattern produced by patterningelement 52. Typically, the DOE generates a two-dimensional array ofM_(x)×M_(y) mutually-adjacent tiles. The multiplication parameters(M_(x), M_(y)) may be chosen as a compromise between the diffractionefficiency, diffraction zero-order intensity, optical design of theprojection lens, and geometrical considerations.

The FOV of the expanded beam transmitted by DOE field multiplier 36 maybe calculated using the grating equation, sin ω′=M sin ω, which givesthe following FOV of beam 38:2ω′_(x)=2arc sin(M _(x) sin ω_(x))2ω′_(y)=2arc sin(M _(y) sin ω_(y))

For example, a 3×3 DOE field multiplier can generate an output FOV of80°×60°, using projection lens 54 with FOV of about 25°×19°. The spatialperiods (d_(x), d_(y)) in the X and Y directions of a DOE made for thispurpose may be calculated from the following expressions:

${d_{x} = {\frac{\lambda}{2\sin\;\omega_{x}} = \frac{\lambda\; M_{x}}{2\sin\;\omega_{x}^{\prime}}}};$$d_{y} = {\frac{\lambda}{2\sin\;\omega_{y}} = \frac{\lambda\; M_{y}}{2\sin\;\omega_{y}^{\prime}}}$wherein λ is the wavelength of light source 50.

Although FIGS. 3A and 3B illustrate the use of a DOE field multiplier inconjunction with a particular beam source configurations, such DOEs maysimilarly be used in other projection assemblies, using other sorts ofbeam sources. Some examples are shown in FIGS. 9A-9C and are describedbelow.

Refractive Field Multipliers

FIGS. 4A and 4B schematically illustrate a field multiplier prism 62, inaccordance with an embodiment of the present invention. FIG. 4A is apictorial illustration, while FIG. 4B is a geometrical representation ofthe prism. Prism 62 may be used as field multiplier 36 in place of theDOE described above in the configurations of projection assembly 30 thatare shown in FIGS. 3A and 3B, for example.

Prism 62 has a triangular profile, typically an isosceles triangle, withan edge 68 that is positioned so that an optical beam 64 projected byprojection lens 54 is incident on the edge and thus on the angled prismfaces on both sides of the edge. The prism generates two outputsub-beams 66, which pass out through a base 69 of the prism (oppositeedge 68) with a total FOV that is expanded by as much as a factor of twoin the direction perpendicular to edge 68. The amount of fieldmultiplication is a function of the vertex angle at edge 68, which istypically greater than 90°, as illustrated in the figures.

As shown in FIG. 4B, the FOV angle ω′ of output sub-beams 66 is afunction of the input FOV ω, the prism angle α, and the correspondingangular refraction parameter β. The relation between these parametersmay be calculated using Snell's law:n sin α=sin(α+ω)   (1)n sin β=sin (α−ω)   (2)sin ω′=n sin(α−β)   (3)

FIG. 4C is a schematic plot containing a curve 65 showing the optimalprism angle α and a curve 67 showing the output FOV full angle 2ω′ as afunction of the input FOV full angle 2ω for prism 62, in accordance withan embodiment of the present invention. In calculating this plot, basedon the above formulas, it was assumed that prism 62 comprises glass witha refractive index of 1.52. With appropriate choice of the prism angle,prism 62 is capable of roughly doubling the FOV of the pattern projectedby lens 54.

FIG. 5 is a schematic side view of projection assembly 30, in accordancewith another embodiment of the present invention, in which a prism 70functions as both field multiplier 36 and beam folder 56. An edge 72 ofprism 70 is positioned in the exit pupil of projection lens 54 andserves to multiply the FOV angle as described above. In addition, theprism comprises an internal reflective surface 74, which folds theprojected optical beam. Thus the projected beam exits prism 70 throughan exit face 76, at right angles to the optical axis of the projectionassembly.

FIG. 6 is a schematic, pictorial illustration of a field multiplierprism 80, which may be used as the field multiplier in projectionassembly 30 in accordance with another embodiment of the presentinvention. Prism 80 has a pyramidal shape with four faces meeting at anapex 86. Prism 80 is positioned so that optical beam 64 projected byprojection lens 54 is incident on the apex. Thus, prism 80 generatesfour output sub-beams 84, which expand the FOV of the projected beam inboth horizontal and vertical dimensions (as opposed to the embodiment ofFIGS. 4A and 4B, which expands the beam in only a single dimension). Aninternal folding surface may be added to prism 80 as in prism 70 (FIG.5).

FIG. 7 is a schematic, pictorial illustration of a field multiplier 90,in accordance with an alternative embodiment of the present invention.Field multiplier 90 comprises two prisms 92, 94, which are similar inshape to prism 62. Prisms 92 and 94 are joined at their respective basesand are rotated relative to one another so that the edges of the twoprisms that are opposite the bases are mutually perpendicular. Thus, theedge of prism 92 expands the FOV of an incident projected beam in onedimension, while the edge of prism 94 expands the beam in the otherdirection.

Integrated Pattern Generators

VCSEL arrays can be used advantageously in producing compact,high-intensity light sources and projectors. In conventional VCSELarrays, the laser diodes are arranged in a regular lattice, such as arectilinear grid pattern as described in the above-mentioned U.S. PatentApplication Publication 2011/0188054, for example, or a hexagonallattice pattern. The term “regular lattice,” as used in the context ofthe present description and in the claims, means a two-dimensionalpattern in which the spacing between adjacent elements in the pattern(for example, between adjacent emitters in a VCSEL array) is constant.The term “regular lattice” in the sense is synonymous with a periodiclattice.

Embodiments of the present invention that are described hereinbelowdepart from this model and instead provide VCSEL arrays in which thelaser diodes are arranged in a pattern that is not a regular lattice.Optics may be coupled to project the pattern of light emitted by theelements of the VCSEL array into space as a pattern of correspondingspots, wherein each spot contains the light emitted by a correspondinglaser diode in the array. Typically (although not necessarily), thepattern of laser diode locations in the array, and hence the pattern ofspots, is uncorrelated, in the sense that the auto-correlation of thepositions of the laser diodes as a function of transverse shift isinsignificant for any shift larger than the diode size. Random,pseudo-random, and quasi-periodic patterns are examples of suchuncorrelated patterns. The projected light pattern will thus beuncorrelated, as well.

Patterned VCSEL arrays of this sort are particularly useful in producingintegrated pattern projection modules, as described below. Such moduleshave the advantages of simplicity of design and production and canachieve cost and size reduction, as well as better performance, incomparison with projection devices that are known in the art.

FIG. 8 is a schematic top view of an optoelectronic device comprising asemiconductor die 100 on which a monolithic array of VCSEL diodes 102has been formed in a two-dimensional pattern that is not a regularlattice, in accordance with an embodiment of the present invention. Thearray is formed on the semiconductor substrate by the same sort ofphotolithographic methods as are used to produce VCSEL arrays that areknown in the art, with suitable thin film layer structures forming thelaser diodes and conductors providing electric power and groundconnections from contact pads 104 to laser diodes 102 in the array.

The non-regular lattice arrangement of FIG. 8 is achieved simply byappropriate design of the photolithographic masks that are used toproduce the array, in any desired two-dimensional pattern.Alternatively, non-regular arrays of other sorts of surface-emittingelements, such as light-emitting diodes (LEDs), may similarly beproduced in this manner (although incoherent light sources, such asLEDs, may be less suitable in some pattern projection applications).

Monolithic VCSEL arrays of the sort shown in FIG. 8 have the advantageof high power scalability. For example, using current technology, a diewith an active area of 0.3 mm² can contain 200 emitters, with a totaloptical power output of about 500 mW or more. The VCSEL diodes emitcircular beams, and may be designed to emit circular Gaussian beams witha single traverse mode, which is advantageous in creating spot patternsof high contrast and high density. Because the VCSEL emission wavelengthis relatively stable as a function of temperature, the spot pattern willlikewise be stable during operation, even without active cooling of thearray.

FIG. 9A is a schematic side view of an integrated optical projectionmodule 110 containing a VCSEL array, such as the array shown in FIG. 8,in accordance with an embodiment of the present invention. VCSEL die 100is typically tested at wafer level, and is then diced and mounted on asuitable sub-mount 114 with appropriate electrical connections 116, 118.The electrical connections, and possibly control circuits (not shown),as well, may be coupled to die 100 by wire bonding conductors 122.

A lens 120, mounted over the die on suitable spacers 122, collects andprojects the output beams of the VCSEL emitters. For temperaturestability, a glass lens may be used. A diffractive optical element (DOE)124, positioned by spacers 126, creates multiple replicas 128 of thepattern, fanning out over an expanded angular range. The DOE may, forexample, comprise a Damman grating or a similar element, as described inthe above-mentioned U.S. Patent Application Publications 2009/0185274and 2010/0284082.

FIG. 10A is a schematic frontal view of an expanded pattern 160projected by optical projection module 110, in accordance with anembodiment of the present invention. This figure shows the sort offan-out pattern that is created by DOE 124. The DOE in this exampleexpands the projected beam into an array of 11×11 tiles 162, centered onrespective axes 164, although larger or smaller numbers of tiles mayalternatively be produced. Each tile 162 (which has the shape of adistorted square, due to pincushion distortion) in FIG. 10A contains apattern of bright spots 166, which is a replica of the pattern of theVCSEL array.

Typically, the fan-out angle between adjacent tiles 162 in this exampleis in the range of 4-8°. Assuming each such tile contains, for example,approximately 200 spots in an uncorrelated pattern, corresponding to theapproximately 200 laser diodes 102 in the VCSEL array, the 11×11 fan-outpattern 160 that is shown in FIG. 10A will then contain more than 20,000spots. DOE 124 is designed so that the projected replicas of the patterntile a surface or region of space, as described, for example, in U.S.Patent Application Publication 2010/0284082.

FIG. 9B is a schematic side view of an integrated optical projectionmodule 130 containing a non-regular VCSEL array, such as the array shownin FIG. 8, in accordance with an alternative embodiment of the presentinvention. In this embodiment, the refractive projection lens 120 ofmodule 110 is replaced by a diffractive lens 130. Lens 130 and a fan-outDOE 134 (similar to DOE 124) may be formed on opposite sides of the sameoptical substrate 132. Although diffractive lenses are sensitive towavelength variations, the relative stability of the wavelength of theVCSEL elements makes this approach feasible. DOE 134 is protected by awindow 138, which is mounted on spacers 140.

FIG. 9C is a schematic side view of an integrated optical projectionmodule 150 containing a non-regular VCSEL array, in accordance with yetanother embodiment of the present invention. Here the functions of thediffractive lens and fan-out DOE are combined in a single diffractiveelement 154, formed on an optical substrate 152, which also serves asthe window. Element 154 performs both focusing and fan-out functions: Itcollects and focuses light emitted by the light-emitting elements on die100 so as to project an optical beam containing a light patterncorresponding to the two-dimensional pattern of the light-emittingelements on the substrate, while expanding the projected optical beam byproducing multiple, mutually-adjacent replicas of the pattern as shownabove.

During assembly of the modules shown in FIGS. 9A-C, the DOE is typicallyaligned in four dimensions (X, Y, Z and rotation) relative to VCSEL die100. The embodiments of 9B and 9C may be advantageous in terms ofalignment, since the photolithographic processes that are used toproduce both the VCSEL array and the DOE/diffractive lens structure areaccurate to about 1 μm, thus permitting passive alignment in X, Y androtation simply by matching fiducial marks. Z-alignment (i.e., thedistance between the VCSEL die and the DOE and lens) requires only asmall range of motion, due to the high accuracy of production.Z-alignment may thus be accomplished either actively, while the VCSELarray is under power, or possibly passively, using a height-measuringdevice, such as a confocal microscope, for example, to measure thedistance between the VCSEL surface and DOE surface.

The modules of FIGS. 9A-C may be used as pattern projectors in 3Dmapping system 20. The tiled pattern (as illustrated in FIG. 10A, forexample) is projected onto an object of interest, and imaging module 32captures an image of the pattern on object 28. As explained earlier, aprocessor associated with the imaging module measures the localtransverse shift of the pattern, relative to a known reference, at eachpoint in the image and thus finds the depth coordinate of that point bytriangulation based on the local shift.

Each replica of the pattern, corresponding to one of tiles 162 in FIG.10A, is internally uncorrelated but is typically highly correlated withthe neighboring tiles. Because each replica of the pattern contains arelatively small number of spots 166, distributed over a relativelysmall angular range, there is a possibility of ambiguity in the depthcoordinates when the transverse shifts of the pattern on the object areon the order of or larger than the pitch of tiles 162. To reduce thisambiguity, VCSEL die 100 may be produced with a larger number of laserdiodes, and the optics of the projection module may thus produce largertiles; but this solution increases the complexity and cost of both theVCSEL die and the optics.

FIG. 10B is a schematic frontal view of an expanded pattern 170projected by an optical projection module, in accordance with analternative embodiment of the present invention that addresses the issueof correlation between neighboring tiles. (The DOE-based fieldmultipliers of FIGS. 3A and 3B may similarly be configured to producepatterns like pattern 160 or 170.) The sort of interleaved tiled patternthat is shown in FIG. 10B is produced by suitable design of the fan-outDOE. In this design, at least some of the tiles in the pattern areoffset transversely relative to neighboring tiles by an offset that is afraction of the pitch. Specifically, in this example, tiles 172 areoffset transversely by half a tile relative to neighboring tiles 174.(The offset is in the vertical direction in this example, on theassumption that only horizontal transverse shift is used in the depthmeasurement).

As a result of this offset between tiles, the range of unambiguous depthmeasurement is effectively doubled. Other interleavings, in whichadjacent tiles are shifted by ⅓ or ¼ of the tile pitch, for instance,can provide even larger ranges of unambiguous measurement. DOEs givingthese and other fan-out patterns may be designed using methods known inthe art, such as methods based on the Gerchberg-Saxton algorithm.

FIG. 11 is a schematic top view of a semiconductor die 180 on which amonolithic VCSEL array has been formed, in accordance with anotherembodiment of the present invention. This array is similar to the arrayof FIG. 8, except that in the embodiment of FIG. 11 there are two groupsof VCSEL diodes 182 and 184, which are driven by separate conductors 186and 188. Diodes 182 and 184 are shown in the figure as having differentshapes, but this shape differentiation is solely for the sake of visualclarity, and in fact, all of the VCSEL diodes in both groups typicallyhave the same shape.

The two groups of VCSEL diodes 182 and 184 that are shown in the figuremay be used, in conjunction with a high-resolution image sensor 42 inimaging module 32 (FIG. 1), to implement a zoom function in depthmapping system 20. The separate power lines feeding the two groups maybe implemented either by providing separate power traces to the twogroups within a single metal layer of the VCSEL die, or by adding ametal layer, so that each group is fed by a different layer. The twogroups may contain the same or different numbers of diodes, depending onthe desired performance characteristics of the system. The image sensoris assumed to support binning of neighboring detector elements (whichprovides enhanced sensitivity and speed at the cost of reducedresolution), cropping of the sensing area, and adjustable clock rate.These features are offered by various commercially-available imagesensors.

In wide-angle mode, one of the two groups of VCSEL diodes (for example,diodes 182) receives power, while the other group is shut off. As aresult, the group that is powered on may be driven at high power, toincrease the brightness of the individual spots in the pattern, withoutexceeding the overall power rating of the VCSEL die. (Higher power peremitter is possible because of the increased distance between the activeneighboring emitters in this mode, which reduces the associated heatingeffect.) Meanwhile, image sensor 42 operates in binning mode, and thusforms a low-resolution image of the entire field of view of the system.Because the detector elements of the image sensor are binned, the imagesensor can capture and output the image at high speed. The processormeasures the transverse shifts of the pattern in this image in order togenerate an initial low-resolution depth map.

The processor may segment and analyze the low-resolution depth map inorder to recognize objects of potential interest, such as a human body,within the field of view. At this stage, the processor may choose tozoom in on an object of interest. For this purpose, the processor turnson all of VCSEL diodes 182 and 184, in both groups, in order to generatea high-resolution pattern. The processor also instructs image sensor 42to operate in cropping mode so as to scan only the area within the fieldof view in which the object of interest was found. The image sensor atthis stage is typically read out at full resolution (within the croppedarea), without binning, and is thus able to capture a high-resolutionimage of the high-resolution pattern. Due to the cropping of the readoutarea, the image sensor is able to output the image at high speed in thehigh-resolution mode, as well. The processor now measures the transverseshifts of the pattern in this latter image in order to form ahigh-resolution depth map of the object of interest.

The embodiment described above makes optimal use of both the powerresources of the VCSEL-based pattern projector and the detectionresources of the image sensor. In both the wide-angle and zoom modes,the scanning speed and sensitivity of the of the image sensor can beadjusted (by binning, cropping, and clock rate adjustment) to providedepth maps of the appropriate resolution, typically at a constant framerate, such as 30 frames/sec.

Although some of the above embodiments refer specifically topattern-based 3D mapping, the pattern projectors described above maysimilarly be used in other applications, including both 2D and 3Dimaging applications, that use patterned light. It will thus beappreciated that the embodiments described above are cited by way ofexample, and that the present invention is not limited to what has beenparticularly shown and described hereinabove. Rather, the scope of thepresent invention includes both combinations and subcombinations of thevarious features described hereinabove, as well as variations andmodifications thereof which would occur to persons skilled in the artupon reading the foregoing description and which are not disclosed inthe prior art.

The invention claimed is:
 1. An optoelectronic device, comprising: asemiconductor substrate; and a monolithic array of light-emittingelements, arranged on the substrate in a two-dimensional pattern that isnot a regular lattice, wherein the two-dimensional pattern of thelight-emitting elements is an uncorrelated pattern.
 2. The deviceaccording to claim 1, wherein the light-emitting elements comprisevertical-cavity surface-emitting laser (VCSEL) diodes.
 3. The deviceaccording to claim 1, and comprising a projection lens, which is mountedon the semiconductor substrate and is configured to collect and focuslight emitted by the light-emitting elements so as to project an opticalbeam containing a light pattern corresponding to the two-dimensionalpattern of the light-emitting elements on the substrate.
 4. The deviceaccording to claim 1, and comprising: a projection lens, which isconfigured to collect and focus light emitted by the light-emittingelements so as to project an optical beam containing a light patterncorresponding to the two-dimensional pattern of the light-emittingelements onto a surface of an object; and an imaging assembly, which isconfigured to capture an image of the projected light pattern on thesurface and to process the image so as to derive a 3D map of thesurface.
 5. A method for producing an optoelectronic device, the methodcomprising: providing a semiconductor substrate; and forming amonolithic array of light-emitting elements on the substrate in atwo-dimensional pattern that is not a regular lattice, wherein thetwo-dimensional pattern of the light-emitting elements is anuncorrelated pattern.
 6. The method according to claim 5, wherein thelight-emitting elements comprise vertical-cavity surface-emitting laser(VCSEL) diodes.
 7. The method according to claim 5, wherein forming themonolithic array comprises forming first and second sets of thelight-emitting elements, wherein the first and second sets areinterleaved on the substrate in respective first and second patterns,and wherein the method comprises separately driving the first and secondsets of the light-emitting elements so that the device selectably emitslight in either or both of the first and second patterns.
 8. The methodaccording to claim 7, and comprising: projecting the light emitted bythe light emitting elements onto an object; capturing first images ofthe object in a low-resolution mode while only the first set of thelight-emitting elements is driven to emit the light, thereby projectinga low-resolution pattern onto the object; and capturing second images ina high-resolution mode while both of the first and second sets of thelight-emitting elements are driven to emit the light, thereby projectinga high-resolution pattern onto the object.
 9. The method according toclaim 5, and comprising mounting a projection lens on the semiconductorsubstrate so as to collect and focus light emitted by the light-emittingelements, thereby projecting an optical beam containing a light patterncorresponding to the two-dimensional pattern of the light-emittingelements on the substrate.
 10. The method according to claim 5, andcomprising: collecting and focusing light emitted by the light-emittingelements so as to project an optical beam containing a light patterncorresponding to the two-dimensional pattern of the light-emittingelements onto a surface of an object; capturing an image of theprojected light pattern on the surface; and processing the image so asto derive a 3D map of the surface.
 11. An optoelectronic device,comprising: a semiconductor substrate; a monolithic array oflight-emitting elements, arranged on the substrate in a two-dimensionalpattern; and a projection lens, which is mounted on the semiconductorsubstrate and is configured to collect and focus light emitted by thelight-emitting elements so as to project an optical beam containing alight pattern corresponding to the two-dimensional pattern of thelight-emitting elements on the substrate.
 12. The device according toclaim 11, and comprising a diffractive optical element (DOE), which ismounted on the substrate and is configured to expand the projectedoptical beam by producing multiple, mutually-adjacent replicas of thepattern.
 13. The device according to claim 12, wherein the projectionlens and the DOE are formed on opposing sides of a single opticalsubstrate.
 14. The device according to claim 11, wherein the projectionlens comprises a diffractive lens.
 15. The device according to claim 11,wherein the projection lens is configured to project the light patternonto a surface of an object, and wherein the apparatus comprises animaging assembly, which is configured to capture an image of theprojected light pattern on the surface and to process the image so as toderive a 3D map of the surface.
 16. A method for producing anoptoelectronic device, the method comprising: providing a semiconductorsubstrate; forming a monolithic array of light-emitting elements on thesubstrate in a two-dimensional pattern; and mounting a projection lenson the semiconductor substrate so as to collect and focus light emittedby the light-emitting elements, thereby projecting an optical beamcontaining a light pattern corresponding to the two-dimensional patternof the light-emitting elements on the substrate.
 17. The methodaccording to claim 16, and comprising mounting a diffractive opticalelement (DOE) on the substrate so as to expand the projected opticalbeam by producing multiple, mutually-adjacent replicas of the pattern.18. The method according to claim 17, wherein the projection lens andthe DOE are formed on opposing sides of a single optical substrate. 19.The method according to claim 16, wherein the projection lens comprisesa diffractive lens.
 20. The method according to claim 16, whereinprojecting the optical beam comprises projecting the light pattern ontoa surface of an object, and wherein the method comprises capturing animage of the projected light pattern on the surface, and processing theimage so as to derive a 3D map of the surface.